| The documented decline in regeneration of sugar maple ( Acer saccharum Marsh.) in northern New England has been blamed on a variety of causes, particularly calcium depletion due to acidic deposition. Alternative factors are also directly and indirectly impacting sugar maple seedling survivorship in the White Mountain region, and are interacting with each other. In particular, I investigated allelopathy, the indirect effects of beech bark disease, ice and wind storm damage, and the legacies of land-use history. Sugar maple seedlings treated with American beech (Fagus grandifolia Ehrl.) leaf leachate had significantly reduced leaf area and biomass than seedlings that were treated with a nutrient control. These results indicate that beech had an allelopathic effect on sugar maple seedling development. Beech bark disease caused increased root sprouting around adult beech that were infected with the disease. In an elimination experiment, I demonstrated that this increased density of beech saplings caused reduced survivorship in sugar maple seedlings, largely due to shading effects. At Hubbard Brook Experimental Forest in West Thornton, NH (43°56′ N, 71°45′ W), the effects of beech bark disease interacted with the ice storm of January 1998 in two distinct ways. First, beech trees most severely damaged by beech bark disease also sustained the most damage from the ice storm. Second, in the newly formed gaps from the ice storm, the advanced regeneration is 74% beech by density, indicating that many of these gaps will likely be filled by beech. To investigate the role of land-use history, I measured tree densities at sites that had been previously logged, used as sugar bushes or were anthropogenically undisturbed. The land-use history determined the density of beech, which played a role in the severity of beech bark disease in the stand. The density of beech, in turn, both played a role in determining the susceptibility of adult beech to ice and wind damage, and also has indirect competitive effects on sugar maple. Therefore, species complexes and the multiple factors that are affecting them need examination if the controls of species distributions and abundances are to be understood. |
